This invention relates generally to injection molding, and more particularly to a thermal gated injection molding nozzle having an integral heating element with an inwardly tapered forward portion which defines a tapered part of the melt channel adjacent the gate.
Thermal gating which is also referred to as temperature assisted gating involves changing the temperature of the melt in the gate area during each cycle to assist in controlling flow to the cavity. This is known in the art such as in U.S. Pat. No. 4,768,945 to Schmidt et al. which issued Sept. 6, 1988 which describes the heating element having a forward portion extending diagonally into a nose portion of the nozzle. In the applicant's U.S. Pat. No. 4,911,636 which issued Mar. 27, 1990 and U.S. Pat. No. 4,941,249 which issued July 17, 1990, thermal gating is described using a nozzle with an integral heating element having a circular portion which encircles the melt bore in a forward nose portion of the nozzle. The applicant's U.S. Pat. No. 4,875,848 which issued Oct. 24, 1989 discloses a tapered gate insert seated in the forward end of a nozzle which is heated by an integral helical heating element.
In all of these previous arrangements, the heating element is embedded in the steel nozzle or gate insert and is not in direct contact with the melt flowing through the melt channel. Thus, when using these previous systems for thermal gating, it has been found that there is a limit on the minimum cycle time because the heating element is embedded in the steel body of the nozzle which acts as a heat sink.